In the memory system of the D. S, Lo, et al., patent, teaching of which is incorporated herein by reference thereto, there is disclosed an oligatomic ferromagnetic film which film is continuous in two orthogonal directions, and which has uniaxial anisotropy providing an easy axis in the plane of the film along which the film's magnetization may be aligned either parallel or antiparallel. Writing of information into the film is accomplished by applying to a small memory area, which area is located at the intersection of a word line and a digit line, a combination of two fields: from the word line an AC hard axis drive field of frequency f of an amplitude that is less than the reversible limit H.sub.R of the memory area; from the digit line, a DC easy axis drive field of a magnitude that is less than the coercive force H.sub.C of the memory area. If the magnetization was previously in the state opposite to the direction of the field from the digit line the memory area is switched (remagnetized) to the opposite information state by the stray field enhanced sequential rotation process. The direction of the resulting remanent magnetization depends on the polarity of the DC easy axis drive field. Non-destructive readout is accomplished by applying the same AC hard axis drive field to the memory area and detecting, on a hard axis aligned sense line, an output signal of frequency 2f.
Subsequent investigation of the switching mechanism of the D. S. Lo, et al., memory system has indicated that the switching astroid is not symmetrical about the orthogonal H.sub.L, H.sub.T axes, and, accordingly, the magnetic domain is subject to erasure under repeated read cycles or to propagation along the word line into the next adjacent memory area. The present invention is directed toward a method of and an apparatus for converting the less stable magnetic domain of the D. S. Lo, et al., patent into a more stable bubble domain using the field stabilizing domain's demagnetizing field and static, alternating-directioned bias fields that lie in the plane of the film and that are substantially parallel or antiparallel to the film's remanent magnetization which is aligned along the film's easy axis.